1. Field of the Invention
The present invention relates to friction coupling assemblies for gear drive units, and more particularly to a friction coupling assembly comprising a fluid pump actuated through an auxiliary clutch and a fluid pressure accumulator charged by the fluid pump for loading a friction clutch.
2. Description of the Prior Art
Conventionally, gear drive units, such as automotive differentials or transfer cases, well known in the prior art, are arranged in a mechanical power transmission system to operatively couple an input shaft to one or more output shafts. Such a device essentially distributes the torque provided by the input shaft between the output shafts. Usually, the gear drive units use a frictional clutch assembly between the input and output shafts. The frictional clutch assembly may be selectively actuated by various hydraulic actuator assemblies. The hydraulic actuator assemblies often include displacement pumps. The displacement pumps are usually in the form of internal gear pumps, such as gerotor pumps adapted to convert rotational work to hydraulic work. In the internal gear pumps, an inner gear having outwardly directed teeth cooperates with an external gear having inwardly directed teeth so that fluid chambers therebetween increase and decrease in volume as the inner and outer gears rotate. By connecting the inlet and outlet of the device to the proper location along the sides of the gear set, the variable displacement chambers receive and discharge hydraulic fluid so that the device can function as a pump. A shaft or other mechanical device can be connected to either the inner or outer gear depending upon the type of device. The hydraulic actuator assemblies further include a hydraulic piston member for frictionally loading the friction clutch.
Recent advances in the art may require the disabling of the 1 frictional clutch assembly in the certain conditions. One such system is the yaw stability control, which uses the vehicle's brakes to correct the trajectory of the vehicle during a turn. The impulse braking of the yaw stability control feature generates a speed difference between the wheels on either side of the vehicle. The limited slip feature will engage due to this speed difference and may interfere with the performance of the yaw stability control feature. There is therefore a need to disable the limited slip feature of the hydraulic limited slip differential during specified conditions to ensure proper performance of the devices like yaw stability control while also allowing the limited slip feature to be enabled at other specified conditions where traction may be needed and where yaw control is not essential. There is a problem with current hydraulically actuated limited slip differentials in that they do not have a simple on/off capability which is separate and distinct from the hydraulic pressure supply/control circuit actuating the clutch assemblies.
It is the intent of this invention to overcome the shortcomings of the prior art by providing an external control of the hydraulic pressure generated within a hydraulically actuated frictional clutch assembly in which the hydraulic pump can either be turned on or off, or set at any intermediate condition by controlling the hydraulic pressure supplied to the clutch actuator.